Every foot is different and all require proper fitting of footwear in order to maintain good foot health. Measurement of the foot has long been done using length and width measurements. Those measurements yield a fair characterization of the general attributes of the foot, but fail to address the unique shape of the undersurface of the foot.
A number of prior art devices have, with varying degrees of success, measured the undersurface of the foot. Optical scanners that use a laser line optic that is projected onto the underside of a foot and a video camera that records the modified location of the reflected line, produce accurate contours. This technique only works well in a non-weightbearing circumstance. The reason is that the foot increases in length by approximately one size (the width also expands) when weight is applied. Measurement of the foot using such a scanner in a non-weight bearing arrangement will result in a data set that does not allow for this natural expansion of the foot in gait.
U.S. Pat. No. 5,689,446 to Sundman et al. and assigned to the same Assignee as this Application, describes a foot contour digitizer wherein a foot is first placed on an array of gauge pins which are in turn deflected to reflect the contour of the underside of the foot. The gauge pins are urged upward by a diaphragm that is moved by air pressure. The deflected gauge pins are then scanned to derive a data set that defines the foot contour.
While the aforementioned measurement device has the advantage of supporting the foot while measurement takes place, the device is inherently expensive, with its hundreds of gauge pins. Details of the gauge pin structure are found in U.S. Pat. No. 4,876,758 to Rollof and assigned to the same Assignee as is this Application.
Franks, in U.S. Pat. No. 4,858,621 discloses a foot pressure measurement system wherein a transparent flat surface is edge-lighted and supports a pliable material on which is placed a foot to be imaged. When the foot applies pressure to the pliable material, an increase in light intensity results in proportion to the pressure, which is sensed by a scanner. The light intensity variations are converted to foot pressure data.
If one places a foot against a transparent flat surface and uses a laser scanner to measure the contour of the undersurface of the foot, the resultant image reflects a contour with large unnatural flat areas of the foot where the foot contacts the transparent surface. Such a device is described in U.S. Pat. Nos. 5,128,880 and 5,237,520 to White.
White discloses a scanner that is similar to a flat plate document scanner, where the undersurface of the foot is imaged in color and the image data is processed to produce elevation data. The White device uses the principle that surfaces that are further away from the contact surface of the scanner will appear darker in the image data.
A problem with the White device is that there is no way to accurately determine the exact distance from the support surface of portions of the foot, using the data which results from the scanned foot image intensities. The variables which act to vary the intensity data include: variations in skin tone and color, ambient light, whether the subject foot is wearing a sock, and the amount of weight applied to the foot. Further, the lowest foot surfaces are whiter in relation to other areas of the foot due to reduced blood flow. Nevertheless, the White structure does exhibit the advantages of: use of an inexpensive flat bed scanner; providing an accurate perimeter of the foot; and providing enough information to characterize certain portions of the foot, e.g. high, low, or sheet arch height.
Even allowing for the variables discussed above, the intensity information acquired from an optical scanner is the sum of three components:
1. The position of the light source relative to the subject surface. PA0 2. The incident angle of light projected onto the subject surface. PA0 3. The distance of the subject surface from the reference surface.
To measure the contour of an object, such as a human foot, the above three components must be taken into consideration. Other variables must be eliminated, or allowed for, to derive accurate elevation data.
Accordingly, it is an object of the invention to provide an improved system for characterizing the undersurface of a foot.
It is another object of the invention to provide an improved system for characterizing the undersurface of a foot that provides consistent intensity data and enables accurate contour data to be derived.
It is a further object of the invention to provide an improved system for characterizing the undersurface of a foot that provides highly accurate foot contour data and enables the production of custom foot supports in accordance therewith.